Interestingly it is also one of the only specific coin designs (that I know of) that's also attested in a written work of history:
"In addition to these activities Brutus stamped upon the coins which were being minted his own likeness and a cap and two daggers, indicating by this and by the inscription that he and Cassius had liberated the fatherland." (Cassius Dio 47.25)
Regarding the spelling EID. (= EIDIBUS, not EDIBUS as the post says), I think there is some evidence that spelling was more conservative in the late Republican period than our manuscripts and editions would indicate (e.g. Quintilian's statement about the use of geminate s in Cicero's time (caussa, cassus, divissiones) which is completely unattested in our manuscripts). Even beyond that, inscriptions and coins tended to conserve archaic spellings more than other texts, and EI for long I is pretty common in inscriptions.
Here's an interesting coin from the Augustan age commemorating an old treaty with Gabii (foedus p.r. qum Gabinis), where "cum" is spelled "qum". Though, as a professor of a friend of mine pointed out, this is less likely to indicate a genuine spelling and more a deliberate attempt at archaism, like saying "ye olde treatie" in English.
I came across the following and wanted to share it too. I considered creating a new thread but then I thought I might as well turn this one into a more general thread. I've changed the title from "Ides of March Coin" to "Ancient Roman Objects".